Magnetic storage devices store data on magnetic media using write heads that generate small magnetic fields. As a write head passes over a medium, its small magnetic field alters localized magnetic moments on the medium. Data is retrieved from magnetic media using read heads that sense transitions in the localized magnetic fields generated by each of these magnetic moments. In response to each of these transitions, a read head generates electrical pulses that are part of a series of pulses forming a read signal. The pulses are either positive or negative depending on the direction of the magnetic moment transition.
Ideally, a read head produces identically shaped pulses for each transition in the magnetic moment. In general, these pulses should be symmetric about their peaks and should have the same general shape during the entire life of the head. However, improperly manufactured heads or heads that have suffered damage may produce excessively asymmetric pulses, may produce different pulse shapes over time, or may produce inconsistent pulse shapes.
New heads that produce excessively asymmetric pulses or existing heads that begin to produce different or inconsistent pulse shapes are sometimes referred to as unstable heads. An unstable head, although functional, is undesirable since it is more likely to fail or "crash". In fact, before crashing, many stable heads become unstable for a period of time.
Since data can be lost when a head crashes, it is desirable to identify unstable heads before they crash. However, the prior art has not provided a method of detecting unstable but functional heads.
The present invention addresses these and other problems, and offers other advantages over the prior art.